Drive clutch

ABSTRACT

A drive clutch having a compressible torque transfer mechanism configured to transfer torque from an engine or motor to a moveable sheave and configured to reduce wear on components of the drive clutch by eliminating sliding contact between surfaces to transfer torque and change the gear ratio. The torque transfer mechanism increases efficiency and reduces wear and may comprise a torque bellows, which is configured to transfer torque from the engine to the moveable sheave upon radial compression of the torque bellows. Sliding blocks and corresponding slide tracks are concentrically positioned between the moveable sheave and the shift plate and centrifugal force provides a force for linear movement for the sliding blocks, which results in movement of the moveable sheave and the cover, which can act to compress the torque bellows. This configuration reduces costs because precise machining is not needed and reduces premature wear and tear on the drive clutch.

BACKGROUND OF THE INVENTION

Various relatively small motorized vehicles, such as snowmobiles,all-terrain vehicles (ATV's), tractors, motor scooters, go-carts andgolf carts use an endless belt type continuously variable transmission(CVT). Variable transmissions include a variable-inputdrive/driving/primary pulley or clutch and an output driven/secondarypulley or clutch. The drive pulley is connected to the crankshaft of theengine. The driving pulley is also called the input pulley because it iswhere the energy from the engine enters the transmission. The secondpulley is called the driven pulley because the first pulley turns it. Asan output pulley, the driven pulley transfers energy to the driveshaftof the track drive. Each pulley is composed of a fixed sheave or pulleyhalf that is fixed in the axial direction, and a movable sheave orpulley half, which is movable in the axial direction. A high strengthmetal or rubber belt, such as a V-belt, joins the drive pulley and thedriven pulley and rides in the groove between the two sheaves. When thetwo sheaves of the pulley are far apart, the belt rides lower in thegroove, and the radius of the belt loop going around the pulley getssmaller. When the sheaves are close together, the belt rides higher inthe groove, and the radius of the belt loop going around the pulley getslarger.

Thus, the effective radius of both the primary and the secondary pulleyis variable. The ratio of the primary pulley radius to the secondarypulley radius determines the ratio of engine rotational speed to thesecondary shaft rate of rotation. When the primary clutch radius issmaller than the secondary clutch radius, the secondary shaft turns at arate that is slower than the engine speed, resulting in a relatively lowvehicle speed. As the ratio of the primary and the secondary clutchradius approaches 1:1, the secondary shaft speed will be approximatelyequal to the engine or crankshaft speed. As the primary pulley radiusbecomes greater than the radius of the secondary clutch, an overdrivecondition exists in which the secondary shaft turns at a greater ratethan the engine crankshaft. CVT's may use hydraulic pressure,centrifugal force or spring pressure to create the force necessary toadjust the pulley halves.

When one pulley increases its radius, the other decreases its radius tokeep the belt tight. As the two pulleys change their radii relative toone another, they create an infinite number of gear ratios—from low tohigh and everything in between. For example, when the pitch radius issmall on the driving pulley and large on the driven pulley, then therotational speed of the driven pulley decreases, resulting in a lowergear. When the pitch radius is large on the driving pulley and small onthe driven pulley, then the rotational speed of the driven pulleyincreases, resulting in a higher gear. Thus, in theory, a CVT has aninfinite number of gears through which it can run at any time, at anyengine speed or at any vehicle speed.

These variable transmissions are equipped with a speed or revolution perminute (RPM) responsive mechanism associated with the drive pulley and atorque responsive mechanism associated with the driven pulley.Therefore, the drive pulley and the driven pulley continuously vary theshift ratio in relation to the drive speed and the driven torque.

The primary clutch is connected to the power source and in theory hasthe job of maintaining the engine's RPM at a value where the most poweris being produced by the engine. The primary clutch may also controlengagement and disengagement of the engine from the load in order tostop and start vehicle movement. In the case of a snowmobile, thesecondary or driven clutch is connected to the load through a jackshaft,gears, chain and track and functions to change the ratio of the twoclutches as the load varies. This function is performed by a torquesensing helix or the like, which is typically considered part of thesecondary clutch.

Prior art clutches are typically of the cam arm and roller type orcomprises a sliding block. The cam arm and roller type clutches areprone to premature wear of the cam arm and the roller, which results inearlier and more frequent replacement. The calibration of force on thebelt can also produce excessive belt heat, which results in beltfailure.

With respect to the sliding block type of clutch, these types ofclutches have calibration characteristics that prevent the clutch fromproducing desired performance. As both types of clutches used today havevarying functional limitations, calibrating a clutch for desiredperformance often results in undesired inherited clutch characteristics.

Drive clutch systems of the prior art lack durability due to wear andtear caused by radial movement from the engine. Engines developinstantaneous RPM changes during operation and produce torsionalvibration and varying inputs. Radial movement, which for purposes ofthis disclosure, comprises torsional vibration, instantaneous RPM andvarying input, causes roller wear and surface deterioration of the camarms as the result of the arms moving across the direction of support ofthe cam arm bearing and the roller bearing. Prior art methods ofminimizing this wear including improving machining tolerance, precisionimprovements to assembly practices and using higher quality material,all of which increase the costs associated with the clutch device.

SUMMARY OF THE INVENTION

An aspect of the present disclosure relates to a drive clutch having atorque transfer mechanism between the engine and the moveable sheaveconfigured to reduce wear on components of the drive clutch byeliminating the sliding contact between a moveable sheave and a driveshaft member. The torque transfer mechanism for increasing efficiencyand reducing wear may comprise a torque bellows, which is configured tomore efficiently transfer torque from the engine to the moveable sheaveupon radial compression of the torque bellows, by being attached to thestationary shaft and the moveable sheave through a cover. Sliding blocksand corresponding slide tracks are concentrically positioned between themoveable sheave and the shift plate and centrifugal force provides aforce for linear movement for the sliding blocks, which results in axialmovement of the moveable sheave, which can act to compress the torquebellows and to move the moveable sheave axially as well as radially.This configuration reduces costs because precise machining is not neededand reduces premature wear and tear on the drive clutch.

Another aspect of the present disclosure relates to monitoring andcontrolling the pressure of a fluid or air sealed in a cavity betweenthe cover and the torque bellows. The torque bellows may be sealed tothe cover by a sealing mechanism and the torque bellows is axiallycompressible along a shaft of the drive clutch. The cavity formed by theshape of the torque bellows may be filled with fluid or air. Compressionof the torque bellows, resulting from axial movement of the drive clutchcomponents during operating, thus changes the fluid or air pressurewithin the cavity. When the cavity is filled with a fluid or air andsealed, the pressure can be gauged and monitored and changes to pressureand volume can be made to adjust functional parameters of the driveclutch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a drive clutch according to the presentdisclosure.

FIG. 2 is an alternative exploded view of the drive clutch.

FIG. 3 is a cross-sectional side-view of the drive clutch assembled.

FIG. 4 is side perspective view of a slide block of the drive clutch.

FIG. 5A is a bottom view of a torque bellows of the drive clutch.

FIG. 5B is a top view of the torque bellows of the drive clutch.

FIG. 5C is a side perspective view of the torque bellows of the driveclutch.

FIG. 5D is a bottom perspective view of the torque bellows of the driveclutch.

FIG. 6A-B are perspective views of the torque bellows when compressed.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure is directed to a clutch assembly for belt-typecontinuously variable transmissions (CVT) which are used in relativelysmall motorized vehicles, such as snowmobiles, all-terrain vehicles(ATV's), tractors, motor scooters, go-carts and golf carts. The clutchassembly of the present disclosure is configured to more effectivelytransfer torque from an engine to a moveable sheave of the clutchassembly. In one embodiment of the present disclosure, the clutchassembly incorporates a torque bellows. The torque bellows iscompressible and compression of the torque bellows results from thetransfer of torque from the engine to the moveable sheave. Thisdisclosure is further directed to a method of controlling the forcesgenerated by shift blocks by incorporating a control mechanism. Thecontrol mechanism may comprise a control device such as a modulator. Itis further contemplated that an interface of the control device can beoperable with various smart systems (electronics) of the engine andmotorized vehicles including other electronic devices.

FIG. 1 is an exploded view of an embodiment of the drive clutch 10 ofthe present disclosure. In one example of the clutch 10, a shaft 20carries a frusto-conical movable sheave 12 and a frusto-conical axiallyfixed sheave 14. Movable sheave 12 includes a belt surface 16 and thefixed sheave 14 includes belt surface 18. A V-belt 19 rides between beltsurfaces 16, 18. During operation of a snowmobile or other vehicle, aspower is applied to the engine, throw weights or sliding blocks 22,which are integral to the drive clutch 10 act to squeeze the sheaves 12,14 toward each other. The squeezing of the sheaves 12, 14 of the driveclutch 10 in turn move the V-belt outwardly toward the exteriorcircumference of the sheaves 12, 14 of the drive clutch 10. The movementof the V-belt 19 outwardly relative to the drive clutch 10 sheaves 12,14 in turn causes the V-belt 19 to be drawn inwardly relative to thesheaves of the driven or secondary clutch. The sheaves of the driven orsecondary clutch then separate. The separation of the driven sheaves inturn changes a gear ratio of the snowmobile.

The following description is in particular to the operation of driveclutch 10, which is mounted to the engine by shaft 20. The taper of theshaft 20 corresponds to the engine's taper shape and transmits enginepower to the clutch 10. As the engine RPM increases, sliding blocks 22are incorporated to produce the force against the shift plate 26. Theamount of force required to produce shifting action is tuned orcalibrated to be exact, however embodiments of the present disclosureproduces additional force, or a force greater than is required forshifting. This force is resisted which allows a control device, forexample, a modulator, to be used to produce the selected shifting actionas will be discussed further below.

This force overcomes the resistance of a return spring 28 and applies anaxial force that moves the movable sheave 12 against the drive belt,which rides between belt surfaces 16 and 18, toward fixed sheave 14 andstarts the shift function. Thus, torque is transferred from the engineto the shaft 20 such that the torque transfer path is through the shaft20, to the shift plate 26, to the torque bellows 24, to the cover 31,and back to the movable sheave 12. The force applied to the belt isgenerated by the shift blocks 22 which slide between inclined shiftramps 23 and the shift plate 20, where the return spring 28 acts againstthis applied force. Spring resistance sets the engagement force and RPM.The spring 28 also generates a subtractive force on the belt. Typically,the force needed for a required shift pattern is a balance of the weightof the cam arm or shift block and the spring. Embodiments of the presentdisclosure can advantageously utilize this force when the torque bellows24 is attached to the sheave 12 and the torque bellows is unsealed, thatis in embodiments where no o-ring 32 is present to seal the connectionof torque bellows 24 to the shaft 20 extending through the aperture andalong which the torque bellows is axially compressible.

The shaft 20 supports the torque bellows 24, which is a torque transfermechanism and may be positioned such that a cover plate 31 may bepositioned to selectively seal off an open space or internal cavity 25of the torque bellows 24. Alternatively, the torque bellows may remainunsealed. The cover plate 31 may comprise, for example, a metal materialor a manufactured plastic material. Further, a spring 28 may bepositioned on the shaft 20 between the shift plate 26 and the torquebellows 24 for a counter force for compressing the torque bellows 24.

As illustrated in FIGS. 1-2, the torque bellows 24 is positioned on theshaft between the shift plate 26 and cover plate 31. A clamp 37 ispositioned between the cover plate 31 and the torque bellows 24 to clampthe torque bellows 24 to the shift plate 26, which is secured in thedrive clutch around the shaft 20. The clamp 37, which may be forexample, a washer, is configured to engage with the shift plate 26 atcollar 26 a and the spring 28 is positioned within this collar 26 a andin connection with the torque bellows 24. Spacer 32 may or may not beincorporated into the drive clutch 10, however as illustrated, spacer 32is configured to allow for adjustment of the load of the spring 28,which sets an engagement point. The torque bellows 24 is attached to thesheave 12 in a manner that allows the parts to be radially movable. Forexample, the torque bellows 24 has an aperture 24 a generally centeredin the concave outer surface near allowing the torque bellows 24 to besecured around the shaft 20.

Thus, the torque bellows 24 is configured to more effectively transfertorque from the engine to the movable sheave 12 and is a component thatis flexible in an axial direction while being rigid in a radialdirection. The torque bellows 24 is compressed as a result of torquetransfer and this compression can be externally modulated. The torquebellows 24 and spring 28 may each change the pressure and volume withinthe cavity 25 and thus change the effect of the spring rate. Forexample, the sealed torque bellows 24 has a volume and pressure that canbe adjusted by a controller or the modulator, and this adjustment allowsthe spring rate to be adjusted by, for example, 50 lbs.

In the embodiment illustrated and as shown in FIGS. 5A to 6B, the torquebellows 24 is a concave component having an outer diameter substantiallyequal to or slightly less than the diameter of the cover 31. Whileembodiments of the present disclosure illustrate the torque bellows 24,other designs that effectively transfer torque while eliminating thesurface contact between the moveable sheave 12 and the shift plate 20can be incorporated. The torque bellows 24 is generally “bowl shaped”and comprises a resilient material that allows the torque bellow to beaxially compressible and radially fixed. In the embodiment illustrated,the torque bellows 24 is comprised of rubber which allows the bellows tobe sufficiently sturdy and to withstand internal pressure changes in theconcave area when sealed and remain resilient when pressure is appliedto compress the torque bellow and released to allow the torque bellows24 to return to its standard shape.

The movable sheave 12 is axially moveable and is moveable against thereturn spring 28 in one direction. This movement results in compressionof the torque bellows 24 in one direction. An outer side or surface ofthe torque bellows 24 is attached to the cover 31, which acts toselectively seal torque bellow cavity 25 and this plate 31 may also actas a clamping mechanism. The drive clutch 10 may operate with a sealedcavity 25 or an unsealed cavity 25.

As illustrated in the figures, the cavity 25, which is an inner area orconcave part of torque bellows 24 may be sealed or unsealed. The volumeof the cavity 25 is changed as the torque bellows 24 is compressed. Whenunsealed, the torque bellows 24 operates to balance the force ofweights, which move the moveable sheave, with the spring force at thesame time torque is transferred from the engine to the movable sheave.When sealed, the volume and pressure inside the cavity 25 can beexternally modulated.

As the torque bellows 24 and the cover 31 may be positioned to seal thecavity 25, forming an interior area where pressure can be adjusted byconnection to an external source of pressure or a relief valve forcontrolling the pressure in the interior are. Altering this pressuringcauses the shift pattern to be selectively changed as a function of thecontrol mechanism. For example, the pressure can be varied by enginevacuum and modulated by the electronic controls of the engine.

The return spring 28 configuration is a steel compression spring incontact with the torque bellows 24 at or near aperture 24 a. The returnspring 28 aids with external modulation of the shift rate and as thetorque bellows 24 is compressed and the spring force is resisted, thevolume of the torque bellows can be modulated. For example, introducinga vacuum effectively decreases the spring force in a sealed cavity 25.The modulation may be generated by increasing or decreasing the pressurewithin the torque bellows 24 by means of air or fluid, where forexample, the volume can be changed within the interior 25. A valve maybe provided to control internal pressure. An example of a suitable valveis a solenoid whose operation is controlled by the electronic controlunit (or “ECU”) of the engine. This control unit may, in some examples,comprise a modulator. Another electrical method of modulation uses apiezoelectric device embedded on the surface of the torque bellows 24.

The torque produced by the engine is transmitted to the moveable sheave12, however the torque bellows 24 and spring 28, which compress anddecompress when the moveable sheave 12 is displaced by outward andinward movement of weights or sliding blocks as discussed further below,the torque transfer mechanism allows for more efficient torque transferfrom the engine to the moveable sheave and a reduction in wear and tearon the drive clutch parts. The assembly reduces the contacting ofsliding radial surfaces, which allows for a reduction in clutch failuresand in clutch function related to slip and stick malfunctions. As thetorque bellows eliminates this sliding contact between two surfaces totransfer torque, the associated effects of radial movement between thesliding surfaces are reduced or eliminated. The drive clutch is furtherconfigured with the torque bellows such that torsional vibrations due toinstantaneous RPM changes during operation and the noise associatedtherewith are reduced.

In further detail, sliding blocks 22 and outwardly inclined surfacesprovide a track or ramp 23 for each sliding block and limiting thedistance the sliding blocks can move outwardly and inwardly with respectto the shaft 20 are incorporated. Such a configuration is only a singlerepresentative embodiment of the invention. In alternative embodiments,cam arm and cam ball assemblies may be used or other methods ofdistributing the force can be incorporated. An odd number of slidingblocks may be used to contribute to rotational stability. A concentricand evenly spaced arrangement of sliding blocks 22 around the shaft 20allows balance and efficiency to be maintained within the drive clutch10 assembly. In prior art drive clutches, torsional vibrations existwhen in operation and effect the rollers and the cam arm. Thesevibrations cause cam arm wear and failure. Embodiments of the presentdisclosure may incorporate the sliding blocks 22 and corresponding ramps23 for sliding block centrifugal movement which allows the relativemovement of the components as shifting is accomplished with thesesliding blocks acting against a surface with no index preference.

As discussed previously above, the force moves the sheave 12, moving themovable sheave 12 with respect to the stationary sheave 14, the clutchbegins shifting and the torque bellows 24 is axially compressed orcollapsed. When the torque bellows 24 is sealed, the fluid or air in thecavity 25 of the torque bellows 24 will also compress and the pressurewill be increased in concave area 25 of the torque bellows 24 as sealedagainst the cover plate 31. This pressure can be gauged with forexample, a pressure sensor (not shown) in communication with the controldevice or modulator by a flexible hose connection which also allows forfluid or air volume control. The modulator can be configured to changethe volume of the liquid and/or the pressure in the torque bellows inresponse to readings from the sensor. Changing the volume allows therate of the shift pattern to be selectively changed and changing thepressure in the torque bellows 24 allows the operating RPM of the engineto be changed. When an electric motor or similar device is attached tothe modulator, the modulator can be controlled electronically.

An outer cover 30 encloses the drive clutch and covers the torquebellows 24 and interior parts up to the movable shave by beingconfigured to slide over and around the drive clutch componentspositioned on the shaft 20. The cover 30 is positioned such that boltsor another securing mechanism may be utilized to secure the cover 30 tothe moveable sheave which may include a cover bushing 34 and can be usedto seal of and enclose the drive clutch by including seals 36 on theends, such as o-rings.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed:
 1. A drive clutch comprising: a first, axiallystationary sheave; a second, axially moveable sheave; and a torquetransfer mechanism positioned between the first and second sheaves andconfigured to transfer torque from a power source to the second,moveable sheave and the transfer mechanism comprising a compressible,resilient material.
 2. The drive clutch of claim 1, wherein the torquetransfer medium is semispherical in shape and further comprising: acover configured to attach to an open end of the torque transfermechanism to form a cavity wherein pressure in the cavity can beselectively changed.
 3. The drive clutch of claim 2, and furthercomprising a spring force positioned between the first sheave and thetorque transfer mechanism and configured to provide a counter force withrespect to the axially compressible torque transfer mechanism.
 4. Thedrive clutch of claim 2, wherein the torque transfer mechanism cavity issealed.
 5. The drive clutch of claim 2, wherein the torque transfermechanism cavity is unsealed.
 6. The drive clutch of claim 2, wherein afirst aperture is substantially centered in a closed end of thesemi-spherical housing and a second, opposing and aligned aperture issubstantially centered in the cover wherein the apertures togetherprovide an opening configured for receiving a rotatable shaft of thedrive clutch.
 7. The drive clutch of claim 1, wherein the torquetransfer mechanism comprises a rubber material.
 8. The drive clutch ofclaim 1, and further comprising a concentric and evenly spacedarrangement of sliding blocks around the shaft and configured forrelative movement of drive clutch components during shifting.
 9. Atorque transfer mechanism for use in a drive clutch assembly comprising:a substantially semi-spherical housing having a substantially openinterior providing an open space, wherein the housing is axiallycompressible and resilient; a substantially flat cover configured to besecurely attached to an open end of the semi-spherical housing andconfigured to selectively seal off the open space; and wherein the openspace is configured to receive a liquid or gas such that a pressure orvolume in the open space can be selectively changed.
 10. The torquetransfer mechanism of claim 9, wherein the torque transfer mechanismcomprises rubber.
 11. The torque transfer mechanism of claim 9, whereinthe torque transfer mechanism and cover are secured to seal the openspace.
 12. The torque transfer mechanism of claim 9, and furthercomprising: a first aperture substantially centered in a closed end ofthe semi-spherical housing; a second aperture substantially centered inthe cover and aligned with the aperture of the housing; and wherein theapertures provide an opening configured for a rotatable shaft to extendthere through.
 13. The torque transfer mechanism of claim 12, whereinthe housing is axially compressible along an axis extending between thefirst and second apertures.
 14. A method of efficiently transferringtorque for shifting at least one gear with a drive clutch mechanism, themethod comprising: providing a drive clutch assembly comprising anaxially compressible torque transfer mechanism; applying torque to ashaft component of the drive clutch and connected to the torque transfermechanism by running a motor operably connected to the drive clutch;initiating shifting of a gear of the drive clutch; and axiallycompressing the torque transfer mechanism to transfer torque from theengine to a moveable sheave of the drive clutch.
 15. The method of claim14, wherein the torque transfer mechanism comprises a substantiallysemi-spherical housing having a substantially open interior providing anopen space and a substantially flat cover configured to be securelyattached to an open end of the semi-spherical housing and to seal offthe open space.
 16. The method of claim 15, and providing a cover forthe torque transfer mechanism configured to selectively seal an interiorcavity of the torque transfer mechanism.
 17. The method of claim 16, andfurther comprising selectively adjusting pressure within the sealed offinterior cavity of the torque transfer mechanism for selectivelycontrolling drive clutch performance.